Ternary selenides and tellurides of silver and antimony and their preparation



United States Patent I 3,008,797 TERNARY SELENIDES AND TELLURIDES OF SIL- IEIAND AN IlMONY AND THEIR PREPARA Tom A. Bither, 'Jr., Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Oct. 10, 1957, Ser. No. 689,258 6 Claims. (Cl. 23-44) This invention relates to new compositions of matter useful as semi-conductors. More particularly, the invention is directed to novel ternary selenides and tellurides of silver and antimony and to their preparation.

In recent years the field of electronics has made spectacular strides. As a result, research interest in semiconductors and in their use in crystal rectifiers, transistors, and photoconductive and thermoelectric devices has been greatly stimulated. Notwithstanding the industrial progress which has been made in this field, there is still need for better and lower cost semi-conductors. Currently, ultrahigh purity silicon and germanium are the only materials which are being promoted commercially for application in semi-conductor fields. However, silicon of the degree of purity required for many applica tions is costly and difficult to produce; and neither germanium nor silicon possesses the best combination of properties for all recognized semi-conductor applications such as, for example in thermo-electric devices.

Accordingly, an object of this invention is to provide 3,008,797 v1?.aienlzed Nov. 14, .1961

monyof this invention can be made at atmospheric presnovel semi-conductors possessing a combination of properties which make them suitable for many of the known semi-conductor uses and which are readily produced, low in cost,'and made from abundantly available materials. A further object is to provide a method for preparing such novel semi-conductors. Another object is to provide novel ternary compounds possessing a combination of carrier mobility, thermal conductivity, and thermoelectric power which makes them especially suitable for interconverting heat and electrical energies. Other objects will appear hereinafter. 7

These and other objects are accomplished by the present invention of ternary silver-antimony selenides and tellurides corresponding in composition to the formula AgSbX wherein X is selected from the class consisting of selenium and tellurium.

The ternary selenides and tellurides of silver and antimony of this invention are conveniently prepared by'fusing together the component elements, that is, silver, antimony, and a group VI-A element of atomic number 3452, under a blanket of an inert gas for a period of from 2 to 30 hours. The reaction temperature should be in the range of 300 to 1200 C. Generally, however, it is preferred to employ temperatures above 350 C. in order to increase reaction rate and hence decrease time of reaction, and below 1000 C. to minimize any tendency of the formed selenides or tellurides todecompose. Since the best balance of reaction rate with yield of desired products is realized within the range of 400 to 1000 C. this embraces the temperature conditions generally employed.

In preparing the ternary compounds of this invention the silver and antimony are mixed in such proportions as to provide a gram atom ratio of 1:1. The selenium or tellurium is provided in amount suchas to have in'the final composition at least two gram atoms per gram atom of silver. These proportions can be obtained l) by using sure, or in closcdreactors under autogenous pressure.

They can also be made uirder super-pressures provided I by an inertgas such as argon;

The ternary selenides ortellurid'es ofv silver and antimoney of this invention are useful in such devices as crystal rectifiers, transistors, and in thermoelectric and other semiconductor devices.

The periodic table referred toin this specification is that published in Demings General Chemistry, 5th Ed, John Wiley & Sons.

The examples which follow illustrate but do not limit this invention. The -Xray diffraction data given therein were obtained by the Debye-Scherrer powder method with a North American Philips unit, using copper KOt-Tfldifltion filtered through nickel to give an effective wave length of 1.542 A. units. .In this method the sample is finely ground and packed into a capillary tube, whichis mounted in a camera having a 114.9 mm. diameter.

In the tabulations of the diffraction data, the heading 1" refers tothe. observedintensity values and d to the interplanar spacings expressed in angstrom. (A.) units. The letter S designatesthe strongest line recorded; M M M and M are'lines of medium intensity, the order of intensity decreasing with increasing numerical sequence; F means thatthe'line is faint; and V that it is very weak.

EXAMPLE I A mixture of 1.08 g. of silver"(0.01 mole), 1.22 g. of antimony (0.0l mole), and 2.55 g. of tellurium (0.02 mole) was heated under 1 atmosphere of argon for 7.75 hours to 938 C. and then allowed to cool to room temperature. The reactantslrad fused to a silvery, metallicappearing, crystalline mass. An X-ray diffraction powder pattern of this material, after subtraction of a trace V V g 3. 62. S 3.05 S- 2.15 V- 1.83 M; 1.76 Ma 1. 52'

.v 1. 39 M1 1.36 Y M2v 1:24

.V 1.170 F 1.078 -V 1. 035 1 M4 1-016 M4 0.963 Mr- 0.919 V 0.879 "Ml- 0. 844 M4 1 0.814

This patternhas no counterpartv in the ASTM (American Society for. Testing Materials) file of known. X-ray diffraction data; v

Analysis indicated the composition to correspond to A r' Analysis-Calcdfor AgSbTe Ag, 22.25; Sb, 25.11; Te, 52.64. Found; Ag, 22.5.8; Sb, 25.01;Te, 52.17.

X-ray diliraction powder patterns runon melt fusions of the blends 3Ag'/Sb/3Te, (3Ag Te/Sb Te and -Ag/.3Sb-/5?I-Te,.. (Ag Telltsb Te showed mixtures of V AgSb'Ee plus AgzTe-and A-gSbTe, plusSb Te Thermal analysis indicated that the compound AgS bTe Q Resistivity: 0.008 ohm. cm.

Thermoelectric power: 300 ;/.v./ C., the hot junction being negative.

Hall coefiicient: 11.6 crn. coulomb, using the sign convention given by Equation 5b-283 on page 5-98 of the American Institute of Physics Handbook (McGraw- Hill, 1957 Thermal conductivity at 25 C.: 0.080 watts./ cm. C.

Energy gap (infrared): 0.1 e.v.

A mixture of 1.08 g. of silver (0.01 mole), 1.22 g. of antimony (0.01 mole), and 1.58 g. of selenium (0.02

mole) was heated under 1 atmosphere of argon for 8 1 hours to 950 C. and then allowed to cool to room temperature. The reactants had fused to a silvery, metallicappearing crystalline mass. An X-ray diffraction powder pattern of this material, after subtraction of trace amounts of silver selenide and antimony, showed the presence of a a new phase. The X-ray diffraction data are tabulated below:

X-ray patternAgS'bSe This pattern finds no counterpart in the ASTM file of known X-ray difiraction data.

The crystal structure of this new phase was identified A y as the cubic sodium chloride type with a value of n equal to 5.80 A. Analysis indicated the composition to correspond to AgSbSe Analysis.-Calcd for AgSbSe Ag, 27.84; Sb, 31.42;

Se, 40.75. Found: Ag, 27.91; Sb, 30.95; Se, 40.98.

X-ray diffraction powder patterns run on melt fusions of the blends 3Ag/Sb/3Se, (3Ag- Se/Sb Se and Ag/3Sb/5Se, (Ag Se/3Sb Se showed mixtures of AgSbSe plus Ag Se and AgSbSe plus Sb Se Thermal analysis indicated that the compound AgSbSe Q 1 melted congr uently at approximately 632 C.

Single crystal of AgSbSe A single crystal was melt grown in the manner described for AgSbTe The maximum temperature of the gradient was 708 C.

Characterization of AgSbSe .--The following properties were determined on sections of the above-described single crystal of AgSbSe tion being the same as in Example I.

The foregoing detailed description-has been given for clearness of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described for obvious modifications will occur to those skilled in the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined a follows.

I claim:

1. A ternary compound corresponding to the formula AgSbXi wherein X is a member of the group consisting of selenium and tellurium,

2. Silver antimony selenide represented by the formula AgSbSe 3. Silver antimony telluride represented by the formula AgSbTe 4. Process for preparing a ternary compound corresponding to the formula wherein X is a member of the group consisting of selenium and tellurium, which comprises heating for a period of from two to thirty hours at a temperature within the range of 300 to 1200 C. silver and antimony in contact with an element selected from the group consisting of selenium and tellurium, said silver, antimony and said element being present in the reaction mixture in such proportions as to provide in the resultant compound a gram atom ratio of silverzantimonyzsaid element of 1:1:2.

5. Process for preparing a ternary compound corresponding to the formula AgSbX wherein X is a member of the group consisting of selenium and tellurium, which comprises heating for a period of from 2 to 30 hours at a temperature within the range of 400 to 1000 C. silver and antimony in contact with an element selected from the group consisting of selenium and tellurium, said silver, antimony and said 'element being present in the reaction mixture in such proportions as to provide in the resultant compound a gram atom ratio of silverzantimony: said element of 1:1:2, and then cooling the resulting ternary compound.

6. Process for preparing a ternary compound corresponding to the formula wherein X is a member of the group consisting of selenium and tellurium, which comprises heating fora period of from 2 to 30 hours at a temperature within the range of 400 to 1000 C. and under superatmospheric pressure, said pressure being provided by an inert gas, silver and antimony in contact with an element selected from the group consisting of selenium and tellurium, said silver, antimony and said element being present in the reaction mixture in such proportions as to provide in the resultant compound a gram atom ratio of silverzantirnony: said element of 1:112, and then cooling the resulting ternary compound.

References Cited in the file of this patent UNITED STATES PATENTS 2,602,095 Faus July 1, 1952 2,728,637 Alderson et a1 Dec. 27, 1955 2,770,528 Maynard Nov. 13, 1956 2,882,467 Wernick Apr. 14, 1959 2,882,468 Wernick Apr. 14, 1959 OTHER REFERENCES Graham in Chemical Abstracts, vol. 47, col. 7953(H) 1953.

Hoffman: Lexikon de Inorgan. Verbindungen: Band I, 2 Halfte Quecksilber Bar No. 32-55, page 1205 (1919). 

1. A TERNARY COMPOUND CORRESPONDING TO THE FORMULA 